Furnace assembly for thermal analysis use

ABSTRACT

This invention relates to a heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace is a radiant heating device utilizing glow bar-type heating rods, with or without an adjacent reflective surface and is adapted to be controlled by means of temperature sensing means disposed within a separate thermal analysis cell which is adapted to be disposed within the furnace.

United States Patent lnventor Horst G. Langer Wayland, Mass.

Appl. No. 848,232

Filed Aug. 7, 1969 Patented Feb. 2, 1971 Assignee The Dow Chemical Company Midland, Mich.

a corporation of Delaware FURNACE ASSEMBLY FOR THERMADANALYSIS USE 6 Claims, 3 Drawing Figs.

US. Cl 13/31, 250/419 Int. Cl l-l05b 3/00 Field of Search 13/31, 20, 25; 250/41.9ISR, C

[56] References Cited UNITED STATES PATENTS 2,971,039 2/1961 Westeren 13/25 3,257,492 6/1966 Westeren l3/25X Primary Examiner- Bernard A. Gilheany Assistant Examiner-Roy N Envall, Jr. Att0rneys-Griswold and Burdick and Earl D. Ayers ABSTRACT: This invention relates to a heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace is a radiant heating device utilizing glow bar-type heating rods, with or without an adjacent reflective surface and is adapted to be controlled by means of temperature sensing means disposed within a separate thermal analysis cell which is adapted to be disposed within the furnace.

Mass s oec/rome/er FURNACE ASSEMBLY FOR THERMAL ANALYSIS USE BACKGROUND OF THE INVENTION This invention relates to radiant-heated furnaces adapted to receive a thermal analysis cell and particularly to furnace and cell insertion assemblies which are adapted for use under high vacuum conditions.

Accordingly, a principal object of this invention is to provide an improved thermal analysis receiving and heating assembly for use under high vacuum conditions Another object of thisinvention is to provide an improved radiant-heating furnace and thermal analysis cell receiving assembly for use under high vacuum conditions in a mass spectrometer.

Even though mass spectrometers are sometimes equipped with devices which allow the heating of samples within the confinement of the mass spectrometer vacuum or within the ion source, and even if such devices sometimes also allow the measurement of sample temperatures during the heating process, these devices do not allow the operation known as thermal analysis. In such high vacuum operations it is essential that the sample be heated at a linear predetermined rate of heating, that the sample temperature is known and indicated at all times, and for differential thermal analysis operations the sample temperature is continuously compared with that of an inert material in the same cell. In general, this requires that three thermocouples located in the thermal analysis cell should be precisely at the same temperature at all times unless a chemical reaction occurs in the sample. Thus, it is also of extreme importance that equalheat transfer is guaranteed from the heat source furnace to the thermal analysis cell, that no temperature gradient exists in the cell itself, that fast heat transfer is provided from the cell to the sample and that each thermocouple remains electrically insulated.

In addition, to make a cell useful it must be possible to load a sample into the cell and introduce the cell with the sample into a mass spectrometer without shutting down the operation of a mass spectrometer or other evacuated systems.

In accordance with this invention, there is provided a furnace which is generally cylindrical in overall configuration and is supported by thermally insulating means attached to a valved tubular thermal analysis cell input and sealing assembly.

The furnace has a symmetrical array of glow bar-type heating elements surrounding an open central axial part into which a differential thermal analysis cell is inserted. Heat reflective elements may be disposed adjacent to the glow bar elements to direct heat towards the above-mentioned cell.

The assembly is inserted into a mass spectrometer adjacent to the ion source.

The invention, as well as additional objects and advantages thereof will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. I is a diagrammatical view showing apparatus in accordance with this invention coupled to a mass spectrometer;

FIG. 2 is a side elevational view, partly in section, of a furnace and cell probe insertion and sealing assembly in accordance with this invention; and

FIG. 3 is a sectional view taken along the line 3.3 of FIG. 2.

Referring to the drawing, and particularly to FIG. 1, there is shown a mass spectrometer 12 having a tubular member 14 extending perpendicularly therefrom. An additional tubular element 42 having a compression coupling 44 at its outer end and having a ball-type vacuum sealing valve 40 adjacent to the member 14 is coupled to the outer end of the member 14. A cell-probe assembly 46 (See FIG. 2) is shown partly inserted into the entry and sealing assembly. A diffusion pump 52 is coupled by means of valve 54 and tube 56 to a fore pump 58 and by means of a tube 60 and valve 62 to the mass spectrometer 12. The tubular element 42 is coupled through tube 48 and valve 50 to the tube 56 between the valve 54 and the fore pump 58.

Referring now to FIG. 2 and FIG. 3, as well as to FIG. 1.

there is shown the mass spectrometer tube I2 having a tubular member 14 extending transversely therefrom adjacent to the ion source 22 of the mass spectrometer. The member 14 has an outwardly extending flange 16 at its outer end. A metal plate 18 on which is supported the furnace and cell probe entry and sealing assembly 10 is sealed, as by the fillet 20, for example, to the flange 16. A threaded tube 68 extends transversely through the plate 18 generally in coaxial relationship with the member 14. A tubular element 42 containing a socalled vacuum ball valve 40 is coupled to the tube 68 by means of coupling 66. A seal-nut element 64 seals the tube 68 and element 42 (and coupling 66) against the plate 18 through which the tube 68 passes.

A coupling 30 having a-flange element 28 welded thereto as at 32 is threadedly coupled to the end of the tube 68 which lies within the tubular member 14. A metal annular plate 92, usually copper or brass and of substantially, larger diameter than the diameter of the coupling 30 is coupled to the top of the flange element 28 by means of screws 34 and insulating spacer elements 26.

An annular-supporting sleeve 94 made of electrically insulating material and is supported from the plate 92 to which it is secured by screws.

An annular plate 74, usually made of metal and at least approximately of the same outer dimension as the diameter of the annular plate 92, is disposed parallel to the plate 92 and is secured to the supporting sleeve 94 by screws 36.

An array of electrical glow bar-heating elements 38a, 38b, and 38c are disposed between the annular plates 74, 92 and are disposed so that the cell 46 may pass within the array without touching the support rods. Elongated heat reflective elements 70a, 70b, and 700 are disposed behind the glow bar elements 38a, 38b, and 38c, respectively.

Wire leads 86a, 88a from the elements 74, 72 are coupled to insulated feed through lines 86, 88, respectively, and thence to a suitable electrical energization source (not shown).

In operation, with the mass spectrometer pumped down by the diffusion pump 52 and with valves 40 and 54 closed, the cell-probe 46 is inserted in the tubular element 42 between the closed valve 40 and the opened compression fitting 44. The compression fitting is then tightened around the tube of the probe 46 and, after a sufficient reduction of pressure by means of the fore pump 58, the valve 50 is closed and ball valve 40 and valve 62 are opened. The cell-probe 46 is then slowly pushed through and past the compression fitting 44, past the valve 40 and into the bore in the furnace body inside of the glow bar array 38a, 38b, 380. The glow bar elements are energized at a controlled rate from a controller energization source (not shown) in coordination with the readings from control thermocouplesor other temperature sensing means in the sample cell-probe assembly 46, as is known to those skilled in the art of differential thermal analysis.

Because of the location of the furnace adjacent to the ion source 22, the material vaporized on heating of the sample material carried in the cell-probe 46 is emitted into the ion source area of the mass spectrometer, where the vaporized material is ionized arid analysis of the sample by mass spectrometric means occurs simultaneously with the differential thermal analysis of the sample.

A cell-probe assembly which is adapted for use with this invention is disclosed and claimed in Horst G. Langer et al. copending application Ser. No. 742,869, entitled, Differential Thermal Analysis Cell Assembly," filed Jul. 5, 1968 now abandoned.

The reflective elements 70a, 70b, 70c may be made of an electrically nonconductive material having a heat reflective coating facing the glow bar elements or may be made of metal in event they are electrically insulated from .the elements 74,92.

The glow bar elements may be Nernst glow bars or rods of silicon carbide, for example.

Thesleeve 94rnay-also, if desired, be provided with an in-- ternalheat reflecting surface'or may be eliminated-if the glow bar elements and/or the reflective elements 70a, 70b, 70c-pro- 1 ments electrically'coupled and disposed'perpendicularly with respect to said first disc and secured adjacent to the outer periphery ofsaid first disc, a seconddisc, said second disc being disposed above said first disc and electrically and mechanically coupled to said heating elements, a second tubular element, said second tubular element being axially aligned with a flanged mounting plate, said flanged plate extending transversely from said tubular element means intermediate the ends thereof, said flanged plate being hermetically sealed to said tubular element means, said tubular means having a valve therein on the side :of saidflanged plate remote from said" rodlike heating elements. said tubular element having an inner diameter which is slightly largerthah thediameterof a ther mal analysis cell assembly adapted td be inserted therethroughr-vr, and into thespace within said rodlike heatingelements, means forsealing the tubing means to saidcell assembly and lead means for energizing said heater winding;

2. An assembly in accordance with claim 1*, wherein said means for sealing the tubing means to said cellassembly comprises a compression seal.

3. Anassemblyin accordance with claim 1, wherein a heat reflective surface is disposedadjacent to CZCiiOf said rodlike heating elements and each presents a concave surface to its 5 rodlike heating element.

4. An assembly in accordance with: claim I, wherein a sleeve extends between said'first and second discs.

5. An assembly inaccordance withclairn I, wherein said flanged plate is adapted to be coupled to a mass spectrometer. 6. An assembly'in accordance with claim 4, wherein said.

sleeve has a heat reflective inner surface. 

1. A furnace and sample insertion assembly for use under high vacuum conditions, comprising first tubular means, a first disc having a central bore which is at least as large as the inner diameter of said first tubular means, said first disc being disposed perpendicularly with respect to said first tubular means and secured thereto an array of rodlike heating elements electrically coupled and disposed perpendicularly with respect to said first disc and secured adjacent to the outer periphery of said first disc, a second disc, said second disc being disposed above said first disc and electrically and mechanically coupled to said heating elements, a second tubular element, said second tubular element being axially aligned with a flanged mounting plate, said flanged plate extending transversely from said tubular element means intermediate the ends thereof, said flanged plate being hermetically sealed to said tubular element means, said tubular means having a valve therein on the side of said flanged plate remote from said rodlike heating elements, said tubular element having an inner diameter which is slightly larger than the diameter of a thermal analysis cell assembly adapted to be inserted therethrough and into the space within said rodlike heating elements, means for sealing the tubing means to said cell assembly, and lead means for energizing said heater winding.
 2. An assembly in accordance with claim 1, wherein said means for sealing the tubing means to said cell assembly comprises a compression seal.
 3. An assembly in accordance with claim 1, wherein a heat reflective surface is disposed adjacent to each of said rodlike heating elements and each presents a concave surface to its rodlike heating element.
 4. An assembly in accordance with claim 1, wherein a sleeve extends between said first and second discs.
 5. An assembly in accordance with claim 1, wherein said flanged plate is adapted to be coupled to a mass spectrometer.
 6. An assembly in accordance with claim 4, wherein said sleeve has a heat reflective inner surface. 